The present invention relates to a clamp for dies of injection molding machines, die casting machines or press machines. It and for workpieces of machine tools, especially relates to a retracting clamp, from whose clamp housing a clamp arm extends or retracts, for injection molding machines.
When exchanging dies of a horizontal type injection molding machine, the procedure is as follows. After locating a die transfer platform car along one side of the vertical die-fixing plates, the dies attached to the plates are transferred onto the platform car by a roll-type transfer device. The new dies are then transferred into the space between the die-fixing plates. Although four clamps are usually provided on each of die-fixing plates, two on the lower portion and the other two on the upper portion, according to this arrangement clamp arms of there four clamps disturb the transferring of the dies. In order to avoid this trouble, the retracting clamp is most preferable for injection molding machines.
As an example of the prior apparatus, RETRACTING CLAMP (U.S. Pat. No. 3,724,837) is shown in FIG. 9, but this retracting clamp has the following defects.
(1) The moment arm between the axial pin (124) and the axial pin (128) is equal to approximately 0.6-0.7 of the moment arm between the axial pin (124) and the clamping portion (118). Therefore, as an example, when the cylinder force F equals 1000 kgf, the clamping force f equals 600-700 kgf. So, in order to lengthen the moment arm between the axial pin (128) and the axial pin (124), the total height and configuration of the clamp is enlarged. As described hereinabove, as force magnifying ratio (i.e. the value of f/F) being extremely small, not only the hydraulic cylinder force has to be powerful, but also the total configuration enlarges and the manufacturing cost becomes very expensive.
(2) As this clamp is not provided with a mechanical latching means, when any leakage of hydraulic pressure occurs from the oil supplying piping or the oilseal packing on the piston, the clamping force also decreases. If the die falls off the die-fixing plate it causes damage to the die itself and the machine.